Dynastic Hero is basically identical to the Megadrive Wonderboy in Monsterworld. Anyone who has played this MD classic will know that this is no bad thing - it's one of the strongest titles in the Wonderboy series. However, this version features different characters.
I can only guess that after the PC Engine started to beat the Megadrive in Japan, Sega stopped allowing its licences to be directly ported to rival formats, forcing developer Westone to 'respray' the characters. However, this doesn't effect the gameplay in the slightest.
The game is a very simple platform/action RPG hybrid, very much like Zelda II on the NES and Princess Crown on the Saturn. Each enemy killed drops money, and these funds can be used to buy weapons, armour and other items. There's some (limited) NPC interaction, brief exploration and a few simple logic puzzles. This isn't a game that will tax you as a player, but it's fun regardless.
The visuals are bright and colourful (the Megadrive version is slightly better in this department) but it's the music that really impresses. The standard Megadrive tunes have been upgraded beyond recognition - this really is some of the best videogame music I've ever heard. I've heard that some people prefer the original 'chip tunes' of the Sega version as opposed to the redbook audio of the TG-16 edition - I guess it's all down to personal taste.
To sum up, this is a nice little game that is worth picking up. If you've already downloaded Wonderboy, then there's obviously very little point in purchasing this as well as they're the same game. If I really had to pick between the two versions the MD original would probably edge it, purely because the visuals are slightly better and the 'new' characters in the TG-16 version are a little funny-looking - but it's a close call.